The present invention is in the field of optics and relates generally to methods for producing selected optical patterns in glass. The patterns may comprise visible optical images formed by variations in optical density, patterns formed by refractive index variations, or patterns formed by a combination of optical density and refractive index variations. Products obtainable in accordance with the invention include photographic reproductions in glass, other optical images or patterns of very high resolution, gradient index lenses, diffraction gratings, and a variety of other useful optical devices.
The concept of treating a glass article to develop patterns or photographic images therein is old, an early reference to this concept being provided by U.S. Pat.Nos. 2,326,012 and 2,422,472. These patents disclose a process wherein glass is melted with certain constituents designed to impart photosensitivity to glass articles produced from the melt. Images are then formed directly in the resulting glass by first exposing the glass to light and thereafter heat treating the exposed glass to develop visible images therein. Many subsequent patents directed at improvements upon this concept have issued, a recent example being U.S. Pat. No. 4,017,318.
While the foregoing patents have as their object the formation of images in optical density in glasses, there have also been attempts to form patterns in refractive index in glasses, that is patterns formed by localized modifications in the refractive index of the material. U.S. Pat. No. 4,110,093 and British Pat. No. 1,519,701 describe techinques for forming a refractive index gradient across a glass rod or other article by impregnating a porous glass preform with a refractive-index-modifying dopant. The distribution of the dopant is then adjusted and it is encased in the glass by a consolidating heat treatment. Unfortunately, refractive index patterns which can be so obtained in this manner are limited to those resulting from diffusion processes.
Photolyzable organometallic compounds are known to be useful for the preparation of photosensitive media, and have been considered as an alternative to precious metal-containing emulsions. V. I. Gorunov et al. describe, in Avtometriya (1978) (1) 71-3 [C.A. 89, 97874M], the preparation of light sensitive sheets or films comprising metal carbonyl compounds wherein permanent optical density changes can be induced by exposure and prompt thermal or physical development.
It has also been proposed to deposite metal film patterns on planar substrates such as glass utilizing organometallic compounds including metal carbonyls and metal alkyls. One method for providing such films is laser-induced chemical vapor deposition, as described by S. D. Allen et al., J. Vac. Sci. Technol., 16(2), March/April 1979, page 431. An alternative method involves the use of a laser to induce photolytic decomposition of metal alkyls or metal carbonyls, as disclosed by P. M. George et al., Thin Solid Films, 67 (1980), pages L25-L28, and T. F. Deutsch et al., Appl. Phys. Lett. 35(2), July 15, 1979, pages 175-177.